MEAN stands for MongoDB, express, angularjs and node. It is a very popular stack for Node/JS developers.
You can check out more at mean.io.

Prerequisites

MongoDB is the database of choise for the mean stack. Head over to
MongoDB in order to install it on your stack. Right now
the MongoDB cookbook will install a single instance machine. (Sharded clusters
are coming)

Bootstrapping

After you have MongoDB installed you can continue with bootstrapping a server
(or servers).